Highly flexible stent and method of manufacture

ABSTRACT

Preferred embodiments of a stent with a high degree of flexibility are shown and described. The stent can include a continuous helical winding and at least one bridge. The continuous helical winding has a plurality of circumferential sections that circumscribe a longitudinal axis from a first end to a second end to define a tube. The circumferential sections are spaced apart along the axis. The at least one bridge is configured to connect one circumferential section to an axially-spaced adjacent circumferential section. The at least one bridge extends on a plane generally orthogonal with respect to the axis.

This application claims benefit of priority to U.S. Provisional PatentApplication No. 60/773,379 filed Feb. 14, 2006 which is incorporated byreference in its entirety.

BACKGROUND

It is known in the medical field to utilize an implantable prosthesis tosupport a duct or vessel in a mammalian body. One such prosthesis mayinclude a frame-like structure. Such frame-like structures are commonlyknown as a “stent”, “stent-graft” or “covered stent.” These structuresare referred to collectively herein as a “stent” or an “implantableprosthesis.”

The stent or prosthesis can be utilized to support a duct or vessel inthe mammalian body that suffers from an abnormal widening (e.g., ananeurysm, vessel contraction or lesion such as a stenosis or occlusion),or an abnormal narrowing (e.g, a stricture). Stents are also utilizedwidely in the urethra, esophagus, biliary tract, intestines, arteries,veins, as well as peripheral vessels. The stent can be delivered via asmall incision on a host body. Hence, the use of stents as aminimally-invasive surgical procedure has become widely accepted.

Previously developed stents for use in the biliary, venous, and arterialsystems have been of two broad classes: balloon-expanded andself-expanding. In both of these classes, stents have been made bydifferent techniques, including forming from wire and machining from ahollow tube. Such machining can be done by photo-chemical etching,laser-cutting, stamping, piercing, or other material-removal processes.Other manufacturing techniques have been proposed, such as vacuum orchemical deposition of material or forming a tube of machined flatmaterial, but those “exotic” methods have not been widelycommercialized.

One common form of stent is configured as a series of essentiallyidentical rings connected together to form a lattice-like framework thatdefines a tubular framework. The series of rings may or may not haveconnecting linkages between the adjacent rings. One example does notutilize any connecting linkages between adjacent rings as it relies upona direct connection from one ring to the next ring. It is believed thatmore popular examples utilize connecting linkages between adjacentrings, which can be seen in stent products offered by various companiesin the marketplace.

All of the above stent examples utilize a biocompatible metal alloy(e.g., stainless steel, Nitinol or Elgiloy). The most common metal alloyutilized by these examples is Nitinol, which has strong shape memorycharacteristics so that Nitinol self-expands when placed in the duct orvessel of a mammalian body at normal body temperature. In addition toself-expansion, these stems utilize a series of circular rings placedadjacent to each other to maintain an appropriate longitudinal spacingbetween each rings. Other examples are shown and described in U.S. Pat.Nos. 7,131,993; 5,824,059; and U.S. Patent Publication No. 2003/055485.Examples which use a helical configuration am shown and described, toidentify a few, in U.S. Pat. Nos. 6,117,165; 6,488,703; 6,042,597;5,906,639; 6,053,940; 6,013,854; 6,348,065; 6,923,828; 6,059,808;6,238,409; 6,656,219; 6,053,940; 6,013,854; and 5,800,456.

A need is recognized for a stent that maintains the patency of a vesselwith the ability to adapt to the tortuous anatomy of the host by beinghighly flexible while being loadable into a delivery catheter ofsufficiently small profile and easily deliverable to target site in thevessel or duct by having the ability to navigate tortuous ducts orvessels.

BRIEF SUMMARY OF THE INVENTION

The embodiments described herein relate to various improvements of thestructure of an implantable stent that embodies a helical winding.

One aspect includes a stent with a continuous helical winding and atleast one bridge. The continuous helical winding has a plurality ofcircumferential sections that circumscribe a longitudinal axis from afirst end to a second end to define a tube. The circumferential sectionsare spaced apart along the axis. The at least one bridge is configuredto connect one circumferential section to an axially-spaced adjacentcircumferential section. The at least one bridge extends on a planegenerally orthogonal with respect to the axis.

In yet another aspect, a stent is provided that includes a continuoushelical winding and at least one bridge. The continuous helical windinghas a plurality of circumferential sections that circumscribe alongitudinal axis from a first end to a second end to define a tube. Thecircumferential sections are spaced apart along the axis. The at leastone bridge is configured to connect one circumferential section to anaxially-spaced adjacent circumferential section. Each circumferentialsection has undulations disposed about the tube. The undulations have atleast one strut connected to the bridge where the at least one strut hasa length greater than a length of other struts unconnected to thebridge.

In a further aspect, a stent is provided that includes a continuoushelical winding and at least one bridge. The continuous helical windinghas a plurality of circumferential sections that circumscribe alongitudinal axis from a first end to a second end to define a tube. Thecircumferential sections are spaced apart along the axis, and eachcircumferential section has undulations disposed about the tube. The atleast one bridge is configured to connect one circumferential section toan axially-spaced adjacent circumferential section. The at least onebridge extends on a plane generally orthogonal with respect to the axis,and the bridge has a width greater than a width of any struts thatdefine the undulations.

In yet a further aspect, a stent is provided that includes a continuoushelical winding, at least one bridge, and at least one annular ring. Thecontinuous helical winding has a plurality of circumferential sectionscircumscribing a longitudinal axis from a first end to a second end todefine a tube. The circumferential sections are spaced apart along theaxis. The at least one bridge is configured to connect onecircumferential section to an axially-spaced adjacent circumferentialsection, the at least one bridge extending on a plane generallyorthogonal with respect to the axis. The at least one annular ring isconnected to one of the first and second ends of the continuous helicalwinding.

In another aspect, a stent is provided that includes a continuoushelical winding, and at least one bridge. The helical windingcircumscribes a longitudinal axis from a first end to a second end todefine a tube having a length of about 60 millimeters and an outerdiameter of about 6 millimeters. The at least one bridge connectsportions of the helical winding so that a force required to displace aportion of the helical winding between two fixed portions of the windinglocated about 30 millimeters apart and disposed in a Lumminexx® IIIsheath is less than 3.2 Newton of force for a displacement of about 3millimeters along an axis orthogonal to the axis.

In a different aspect, a method of loading a stent into a generallytubular sheath for delivery into a biological host is provided. Themethod can be achieved by providing a stent including a continuoushelical winding having a plurality of circumferential sectionscircumscribing a longitudinal axis from a first end to a second end todefine a tube, the circumferential sections being spaced apart along theaxis where each of the circumferential sections includes repeatingstruts, and a plurality of bridges, each bridge is configured to connectone circumferential section to an axially-spaced adjacentcircumferential section, the at least one bridge extending on a planegenerally orthogonal with respect to the axis, and compressing the stenthaving an outside diameter of approximately 6 millimeters to fit withinthe generally tubular sheath that has an inside diameter ofapproximately 2 millimeters (about 6 French) without any of the strutsof the stent crossing each other inside the sheath.

In another aspect, a method of loading a stent into a generally tubularsheath for delivery into a biological host is provided. The method canbe achieved by providing undulations configured in a helical path abouta longitudinal axis and configured in a first tubular shape in anexpanded configuration, locating the undulations and bridgesinterconnecting the undulations in a second tubular shape having aninside diameter with respect to the axis of approximately 6 French andin a compressed configuration smaller than the first tubular shape, andpreventing physical interference between portions of the undulations andbridges in the compressed configuration.

These and other embodiments, features and advantages will becomeapparent to those skilled in the art when taken with reference to thefollowing detailed description in conjunction with the accompanyingdrawings that are first briefly described.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings, which are incorporated herein and constitutepart of this specification, illustrate exemplary embodiments of theinvention, and, together with the general description given above andthe detailed description given below, serve to explain the features ofthe invention.

FIG. 1 is a side view of a helical type stent of the preferredembodiment.

FIG. 2 is a perspective view of a portion of the stent of FIG. 1.

FIG. 3 is a close-up, perspective view of the stent of FIG. 2.

FIG. 3A is a close-up, perspective view of an alternate embodiment of abridge connection illustrated in FIG. 3.

FIG. 4 is a close-up side view of a bridge connection of the stent ofFIG. 1.

FIG. 5A is a close-up partial side view of an end portion of the stentof FIG. 1.

FIG. 5B is a close-up partial side view of an end portion of the stentof FIG. 1 in an unexpanded configuration.

FIG. 6 is a close-up partial side view illustrating the loading forcesand distortion of an alternative embodiment of the bridge connection.

FIG. 7 is a close-up partial side view of an embodiment of the stent inan unexpanded configuration.

FIG. 8 is a side view of a portion of an alternative stent to the stentof FIG. 1.

FIG. 9 illustrates a testing stand to determine flexibility of thepreferred stent in a delivery catheter.

FIG. 10 is a side view of a portion of another alternative stent to thestent of FIG. 1.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The following detailed description should be read with reference to thedrawings, in which like elements in different drawings are identicallynumbered. The drawings, which are not necessarily to scale, depictselected embodiments and are not intended to limit the scope of theinvention. The detailed description illustrates by way of example, notby way of limitation, the principles of the invention. This descriptionwill clearly enable one skilled in the art to make and use theinvention, and describes several embodiments, adaptations, variations,alternatives and uses of the invention, including what is presentlybelieved to be the best mode of carrying out the invention.

As used herein, the terms “about” or “approximately” for any numericalvalues or ranges indicate a suitable dimensional tolerance that allowsthe part or collection of components to function for its intendedpurpose as described herein. Also, as used herein, the terms “patient”,“host” and “subject” refer to any human or animal subject and are notintended to limit the systems or methods to human use, although use ofthe subject invention in a human patient represents a preferredembodiment.

Referring to FIGS. 1 and 2, a stent 100 is shown having a tubular shapeand a first end 10, a second end 12, an intermediate portion 14, and alongitudinal axis 16. The intermediate portion 14 includes a continuoushelical winding 18. The winding 18 has a plurality of circumferentialsections 20 (identified as 20 a-20 g in FIG. 1) that join togetherend-to-end and circumscribe the axis 16 from the first end 10 to thesecond end 12, with the continuation of each circumferential section 20along the path of the helical winding 18 represented with dashed linesin FIG. 1. In FIGS. 1, 2, 8, and 10, the portions of the stent 100 (orstents 200 or 300) in the background of the figure are not shown indetail, for clarity and to clearly show identical features alreadypresented in the foreground of the figure. The circumferential sections20 are longitudinally spaced apart along the axis 16 and disposed 360degrees about the axis 16. The axial distances between adjacentcircumferential sections 20 define spacing 22, and the spacing 22 isshown in FIG. 1 with the same dashed lines that represent thecontinuation of the helical winding 18 for each circumferential section20 in the background of the figure. The spacing 22 of eachcircumferential section 20 defines a helical angle 24 relative to aplane collinear with the axis 16 (as shown) or relative to an orthogonalplane intersecting the axis 16, with each circumferential section 20having a helical angle on a first-end facing side and a second-endfacing side. Although only one helical winding 18 is illustrated in FIG.1, more that one helical winding 18 can be employed in the stent 100.For example, a helical winding with a first helical angle can beconnected or coupled with another helical winding that has a differentsecond helical angle. Alternatively, the helical winding 18 of FIG. 1can be utilized as a central portion of the intermediate portion 14 andthe helical winding 218 of the stent 200 illustrated in FIG. 8 can beutilized proximate each end of the intermediate portion 14, and viceversa.

The stent 100 includes at least one bridge 26 configured to connect onecircumferential section 20 to an axially-spaced adjacent circumferentialsection 20. The bridge 26 extends generally circumferentially around theaxis 16 on a generally orthogonal plane with respect to the axis 16.That is, the bridge 26 forms a circumferential connector or bridgemember (i.e., “circumferential bridge”) between circumferential sections20 of the helical winding 18. Preferably, there are a plurality ofbridges 26 interconnecting the circumferential sections 20 to adjacentcircumferential sections 20.

As illustrated in FIG. 3, in the intermediate portion 14, eachcircumferential section 20 includes a plurality of struts 28 joinedtogether by strut vertices 30 and bridge vertices 31 disposed at ends ofthe struts 28. The strut vertices 30 connect two struts 28 together, andthe bridge vertices 31 connect one or two struts 28 and a bridge 26together. The bridge vertices 31 are larger than the strut vertices 30in order to accommodate the connection of the bridges 26 to the struts28. The bridges 26 connect the bridge vertices 31 in one circumferentialsection 20 to the bridge vertices 31 in an adjacent circumferentialsection 20. The bridges 26 provide a circumferential offset, equal tothe length of the bridge 26, between connected bridge vertices 31 thatapproximately face each other across the spacing 22 between adjacentcircumferential sections 20. Upon expansion of the stent 100, thebridges 26 maintain an offset orientation between the bridge vertices31, so that the strut vertices 30 and bridge vertices 31 of onecircumferential section 20 do not abut or near the opposing strutvertices 30 or bridge vertices 31 of an adjacent circumferential section20. Also, when the stent 100 is bent slightly and forced to conform to acurve, the strut vertices 30 and bridge vertices 31 disposed on theinside path of the curve will move towards each other and close thespacing 22 between adjacent circumferential sections 20 (and possiblycontinue moving towards each other so that one circumferential section20 moves into the path of the helical winding 18 occupied in part byanother circumferential section 20), but avoid or minimize directcontact or interference because the bridges 26 cause the strut vertices30 and bridge vertices 31 of one circumferential section 20 tointerdigitate with those of another circumferential section 20. Thisinterdigitation of the circumferential sections 20 allows the stent 100to bend easily without interference between struts 28, strut vertices30, and bridge vertices 31 on adjacent circumferential sections 20 ofthe helical winding 18. That is, each of the bridges 26 is configured sothat the end of the bridge 26 connected to one bridge vertex 31 iscircumferentially aligned with the other end of the bridge 26 connectedto another bridge vertex 31 on a plane that is orthogonal to the axis16, whether the stent 100 is in an expanded or unexpanded configuration.As illustrated in FIG. 3A, an alternative bridge 27 a can be non-linear,but one end of the bridge 276 remains circumferentially aligned with theother end of the bridge 27 c (illustrated by a dashed line betweenbridge ends 27 b and 27 c) in a plane orthogonal to the axis 16. Assuch, the bridge 26 is not required to be linear as illustrated hereinbut can include curved, zig-zag, meandering curves, sinusoidal, orcurvilinear configurations as long as the end points connecting toopposing bridge vertices 31 are aligned with the circumference of a tubedefined by the stent 100. Alternatively, as illustrated in FIG. 3A, thebridges 26 of the various embodiments can also provide an extension 27 dthat permits comparatively slight extension of the stent 100 in thedirection of the axis 16 or beyond the radial periphery of the stent 100defined by the expansion of the circumferential sections 20, asdescribed and shown U.S. patent application Ser. Nos. 11/216,222;11/216,228; 11/216,293; 11/216,362; and Ser. No. 11/216,554 filed onAug. 31, 2005, all of which are incorporated by reference herein intheir entirety.

While providing these aforementioned advantages, the circumferentialbridges 26 provide for a more generally even expansion of the stent 100because some of the bridges 26 are disposed away from the expandingportions of the circumferential sections 20 that define the helicalwinding 18. As illustrated in FIG. 3, in the preferred embodiments, thecircumferential sections 20 have undulations that are formed by thegenerally linear struts 28 coupled together at the strut vertices 30 orbridge vertices 31, which are deformed during expansion and compressionof the stent 100. Where the bridge 26 a is coupled to struts 28 a and 28b in FIG. 3, the bridge vertex 31 a is sufficiently rigid so that itisolates any deformation of the struts 28 a and 28 b (during expansionof the stout 100, for example) from the bridge 26 a, so that bridge 26 ais not or only minimally deformed. Preferably, the stent 100 is aNitinol self-expanding stent of approximately 6 mm final diameter, andthe bridge 26 is approximately 100 microns wide in the direction of theaxis 16, approximately 200 microns thick in the radial direction fromthe axis 16, and approximately 130 microns long in the circumferentialdirection between the bridge vertices 31. The bridge vertices 31,illustrated in FIG. 4, are approximately 90 microns wide in thedirection of axis 16, approximately 200 microns thick in the radialdirection from the axis 16, and approximately 1500 microns long in thecircumferential direction around axis 16. Other materials can be usedinstead of Nitinol, such as, for example, weak shape memory metals(e.g., stainless steel, platinum, Elgiloy), shape memory polymers,bioresorbable metals and polymers.

Referring to FIGS. 1 and 2, it is noted that the number of bridges 26and struts 28 can be varied. In one embodiment, the number of struts 28above and below any bridges 26 (within a single arcuate undulationsection 32) can be the same. An arcuate undulation section 32 is aseries of struts 28 and strut vertices 30 extending between two bridgevertices 31 on a single circumferential section 20. For example, withreference to circumferential section 20 c in FIG. 1, bridge vertices 31a and 31 b have five struts 28 therebetween (which define fiveundulations in the arcuate undulation section 32 a). Bridges 26 c and 26d join the arcuate undulation section 32 a to arcuate undulationsections 32 in adjacent circumferential sections 20 b and 20 d,respectively, which are spaced at a predetermined distance (spacing 22)from circumferential section 20 c. In particular, five struts 28 aredisposed along any one of the arcuate undulation sections 32 between anyone bridge 26 and another next bridge 26 in the intermediate portion 14,in a circumferential direction that is either clockwise orcounter-clockwise around the axis 16. It is believed that a designhaving equal number struts 28 provides advantageous characteristics withregard to flexibility and strength. In the preferred embodiments, thenumber of struts 28 in the clockwise or counterclockwise circumferentialdirections can range from three to nine, inclusive. Alternatively, thenumber of struts 28 in one circumferential direction can be differentfrom the number of struts 28 in the other circumferential direction. Forexample, as illustrated in FIG. 8, there are seven struts 28 disposedbetween bridge vertex 31 c and bridge vertex 31 d in the circumferentialcounter-clockwise direction identified by arrow 34 and five struts 28disposed between bridge vertex 31 c and bridge vertex 31 e in thecircumferential clockwise direction identified by arrow 36. In thepreferred embodiments, a pattern of three struts 28 in thecounter-clockwise direction and five struts 28 in the clockwisedirection from a single bridge vertex 31 (a three-five pattern), afive-five pattern, or a five-seven pattern are utilized.

With reference to FIG. 7, a portion of the stent 100 is shown in acompressed and unimplanted configuration. In order to discuss thevarious features of the struts 28 and bridges 26, the followingdefinition of strut length is used. A “strut length” is the length of astrut 28 from a center 38 of a radius of curvature of one end of thestrut 28 (at a strut vertex 30 or bridge vertex 31) to another center 38of a radius of curvature located on the other end of the strut 28 (at astrut vertex 30 or bridge vertex 31). As such, as illustrated in FIG. 7,the strut length of the strut 28 c (extending between two strut vertices30) is strut length 40 a, the strut length of the strut 28 d (extendingbetween a strut vertex 30 and a portion 42 of a bridge vertex 31) isstrut length 40 b, and the strut length of strut 28 e (extending betweena strut vertex 30 and a portion 43 of a bridge vertex 31) is strutlength 40 c. Portion 43 is disposed more closely to the bridge 26 thanportion 42. Using this definition, it can be seen that strut length 40is greater than strut length 40 b, and that strut length 40 b is greaterthan strut length 40 a. In an alternative embodiment, the strut lengthsof sequential struts 28 in a circumferential section 20 can alternatebetween a relatively short strut 28 and a relatively long strut 28 toallow for the axial advancement of the helical winding 18.

Further, the use of bridges 26 to connect adjacent circumferentialsections 20 is not limited to the configuration illustrated in thefigures but can include other configurations where the bridge 26 is on aplane obliquely intersecting the axis 16 or generally parallel to theaxis 16. For example, as shown in FIG. 10, an alternative stent 300includes an axial bridge 44 extending substantially parallel withrespect to the axis 16 of the stent. Also illustrated is a wave typespring bridge 45 (e.g., curvilinear in profile), an oblique bridge 46extending obliquely with respect to an axis extending parallel to theaxis 16, and a long bridge 47 extending far enough between bridgevertices 31 so that there is a “bypassed” strut vertex 30 or anotherbridge vertex passed by and not engaged with the long bridge 47. As alsoillustrated in FIG. 10, the stent 300 can utilize a combination ofbridge types. Alternatively, the bridges 26, 44, 45, 46, or 47 candirectly connect a peak 48 of one circumferential section 20 to anotherpeak 48 of an adjacent circumferential section, as illustrated byoblique bridge 46. In yet another alternative, the bridges 26, 44, 45,46, or 47 can connect a peak 48 to a trough 50 of an adjacentcircumferential section 20, as illustrated by axial bridge 44 and wavetype spring bridge 45. In a further alternative, the bridges 26, 44, 45,46, or 47 can connect a trough 50 to a trough 50, as illustrated by longbridge 47. Moreover, the undulations of the arcuate undulation section32 can be wave-like in pattern. The wave-like pattern can also begenerally sinusoidal in that the pattern can have the general form of asine wave, whether or not such wave can be defined by a mathematicalfunction. Alternatively, any wave-like form can be employed so long asit has amplitude and displacement. For example, a square wave, saw toothwave, or any applicable wave-like patter defined by the struts where thestruts have substantially equal lengths or unequal lengths. Also thestents 100, 200, or 300 can be stents that are bare, coated, covered,encapsulated, bio-resorbable or any portion of such stents.

It is appreciated that the struts 28 and circumferential sections 20 inthe intermediate portion 14 of the stent 100 are supported directly orindirectly on both axial sides (the sides facing spacing 22) by bridges26 because they fall between other adjacent circumferential sections 20.However, the axially endmost turns of the helical winding 18 (theaxially endmost circumferential sections 20, such as circumferentialsection 20 a in FIG. 1) are supported by bridges 26 only on the side ofthe circumferential section 20 facing another circumferential section20, and these endmost circumferential sections 20 lack bridges 26 on thesides that do not face an adjacent circumferential section 20, which canaffect the proper and even orientation of the struts 28 in these endmostcircumferential sections 20 during the contraction or expansion of thestent 100. Any distortions attributable to this one-sided bridge 26arrangement are small and are usually negligible. However, when markersare attached to the endmost turns of the winding 18 (the endmostcircumferential sections 20) with extensions, the lengths of the markersand the extensions are believed to amplify any distortion of the endmostturns. This unevenness is particularly noticeable in a helical windingbecause the struts are generally of unequal length in order to provide asquare-cut end to the stent, and any small distortions of the endmostturns are amplified to differing degrees by the different lengths ofmarker extensions.

There are several effects of the marker movement referred to above.Cosmetically, the stem can be given a non-uniform appearance that isobjectionable to a clinician. If the distortions are large enough, therecan be interference between or overlapping of the markers. Thesedistortions can arise during manufacture of the stent, when the pro-formof a self-expanded stent is expanded to its final size. Similardistortions can arise when a finished stent is compressed for insertioninto a delivery system, or when a stent is in place in vivo but held ina partially-compressed shape by the anatomy.

Referring to FIGS. 1-3 and particularly 5A-5B, at the first end 10 andsecond end 12 of the stent 100 there are provided markers 60 extendingfrom the strut vertices 30 of the helical winding 18 with extensions 61.Reinforcing or connecting structures 62 are formed in the stent pre-form(i.e., in the initial manufacturing state of the stent 100) andstabilize the shape and orientation of markers 60 during the expansionof the stent 100 and during the manufacture of the stent 100. It isbelieved that these connecting structures 62 serve the additionalfunction of improving the stability of the markers 60 when the stent 100is collapsed for the purpose of delivering the stent to a locationwithin a living body. Further, these connecting structures 62 are alsobelieved to improve the stability of the stent 100 in vivo by improvingthe resistance to deformation of the markers 60.

With the use of the connecting structures 62, the distortions at theends 10 and 12 of the stent 100 can be reduced or mostly eliminated.Specifically, the connecting structure 62 is formed by an annular ring64 that includes a series of end struts 66 and bending segments 68(similar to the struts 28 and strut and bridge vertices 30 and 31) andis connected between adjacent markers 60 in order to present reactiveforces to resist distortion from the expansion and compression of thestruts 28. Because these end struts 66 are connected at an axially outerend of the markers 60, they present the greatest possible leverage tomaintain the longitudinal axial alignment of the markers 60 andextensions 61 while presenting radial compressive and expansion forcessimilar to those of the struts 28. These end struts 66 are cut into thestent pre-form at the same time that the strut 28 and bridge 26 patternof the stent 100 is cut, typically using a laser cutting apparatus or bya suitable forming technique (e.g, etching or EDM). These end struts 66(along with bending segments 68) then tend to hold the markers 60 andthe extensions 61 in parallel or generally in longitudinal axialalignment with the axis 16 when the stent pre-form is expanded duringthe manufacturing process.

Once the stent pre-form has been expanded, the end struts 66 can beeither removed or left in place to form part of the finished stent 100.If it is desired to remove the end struts 66, then the end struts 66 canbe designed with sacrificial points 67, i.e., there can be notches orother weakening features in the body of the end struts 66 where the endstruts 66 attach to the markers 60, so that the end struts 66 can beeasily removed from the stent 100 by cutting or breaking the end struts66 at the sacrificial points.

Alternatively, the end struts 66 can be designed so that they remainpart of the stent 100. In this case, there would be no artificiallyweakened sacrificial point at the connection to the markers 60. Afterthe stent pre-form is expanded, the final manufacturing operations wouldbe completed, including cleaning, heat-treating, deburring, polishing,and final cleaning or coating. The resulting stent can then have the endstruts 66 in place as an integral part of the stent 100 structure.

In the preferred embodiment, shown in FIGS. 5A and 5B, the markers 60are approximately 620 microns wide in the circumferential direction andapproximately 1200 microns long in the direction of axis 16. Mostpreferably, the markers 60 are unitary with the extension 61 of thehelical winding 18, are generally rectangular in configuration, and canhave the inside surface of each marker 60 curved to conform to thetubular form of the stent 100. Alternatively, the markers 60 can beformed as spoon-shaped markers joined to the extensions 61 by welding,bonding, soldering or swaging to portions or ends of the extensions 61.In a further alternative, materials can be removed from either theluminal or abluminal surface of the markers 60 to provide a void, and aradiopaque material can be joined to or filled into the void. Themarkers 60 can be mounted at the end of extensions 61. The end struts 66joining the markers 60 can be approximately 80 microns wide in thecircumferential direction and approximately 1500 microns long in thedirection of the axis 16 when the stent 100 is in a compressed state, asillustrated in FIG. 5B. In the embodiment illustrated in FIGS. 5A and5B, there are four end struts 66 between two adjacent markers 60. In thepreferred embodiments, the rectangular marker 60 can have its lengthextending generally parallel to the axis 16 and its circumferentialwidth being greater than two times the width of any strut 28 (i.e.,circumferential width in the compressed configuration). In oneembodiment, the circumferential width of at least one strut 28 isapproximately 65 microns and the circumferential width of the at leastone strut 28 is approximately 80-95% of a width of the bridge 26 in thedirection of the axis 16.

Referring to FIG. 5B, the structure of the end struts 66 that connect tothe markers 60 are preferably provided with a slight curvature 70 (andcorresponding curvature on the markers 60) to provide for strain reliefas the end struts 66 are expanded.

In an alternative embodiment, the connecting structure 62 includes twoend struts 66 (instead of the four of the preferred embodiment) ofapproximately 90 microns wide in the circumferential direction (when thestent 100 is in the compressed configuration) and approximately 2000microns long in the direction of the axis 16. It should be noted thatfour end struts 66 can be utilized when, for example, no marker 60 isused or only a minimal number of markers 60 are needed. The markers 60in the embodiments are preferably approximately 620 microns wide in thecircumferential direction and approximately 1200 microns long in thedirection of the axis 16. The markers 60 are preferably mounted on theextensions 61 that are approximately 200 microns wide in thecircumferential direction and approximately 2000 microns long in thedirection of the axis 16. Preferably, the stent 100, in the form of abare stent, is manufactured from Nitinol tubing approximately 200microns thick and having an approximate 1730 micron outside diameter,and is preferably designed to have an approximately 6 mm finished,expanded, and unimplanted outside diameter.

There are several features of the stent 100 that are believed to beheretofore unavailable in the art. Consequently, the state of the art isadvanced by virtue of these features, which are discussed below.

First, as noted previously, the continuous helical winding 18 can have aplurality of circumferential sections 20. A plurality of bridges 26extend on a plane generally orthogonal with respect to the axis 16 toconnect the circumferential sections 20. By this configuration of thecircumferential bridges 26 for the helical winding 18, a more uniformexpansion of the stent 100 is achieved.

Second, each of the circumferential sections 20 can be configured asarcuate undulation sections 32 (FIGS. 1 and 2) disposed about the axis16. The arcuate undulation sections 32 can have bridges 26 with struts28 connected thereto so that the struts 28 connecting to the bridges 26have a length greater than a length of other struts 28 that are notconnected directly to the bridges 26. With reference to FIG. 7, it isnoted that the struts 28 can have a strut length 400 that is greaterthan a strut length 40 b, and a strut length 40 b that is greater than astrut length 40 a.

Third, the bridge 26 can be connected to the adjacent arcuate undulationsection 32 at respective locations other than the peaks 48 of theadjacent arcuate undulation section 32. For example, as shown in FIG. 4,the bridge 26 has an axial width selected so that the edges of thebridge 26 form an offset 71 that sets the bridge 26 slightly back fromthe outermost edge 31 f of the bridge vertices 31. By virtue of sucharrangement, distortion is believed to be reduced in the struts 28, andsubstantially reduced at the struts 28 connecting directly to the bridgevertices 31. Specifically, FIG. 6 illustrates the increased bendingstrains placed on the stressed struts 28 f when the bridge 26 isstressed by bending or by torsion of the stent 100. In the exampleillustrated in FIG. 6, a clockwise force is applied in the direction ofthe arrows 72 which results from the bending or torsion of the stent100, and the greatest stresses are believed to be developed athigh-stress points 76 where the stressed struts 28 f connect to thebridge vertices 31. It is believed that distortion of the strut patterncan be expected to result in increased local strains, which can causesmall regions of the strut pattern to experience higher than normalstrains. It is also believed that such increased strains can lead topremature failure in vivo. Because the high-stress points 76 in thepreferred embodiments are located away from the bridge 26 by a distancecorresponding to the circumferential width of the bridge vertex 31, asillustrated in FIG. 6, localized strains at the bridge 26 connectingpoints 74 (where the bridge 26 connects to the bridge vertices 31) areless than those experienced at the high-stress points 76. In addition,the struts 28 can have linear segments, curved segments or a combinationof curved and linear segments. Also, by virtue of the circumferentialbridges 26, the struts 28 can have a curved configuration between peaks48 of a winding 18 as illustrated, for example, in FIG. 6.

Fourth, in the embodiment where a bridge 26 extends on a plane generallyorthogonal with respect to the axis 16, them is at least one annularring 64 connected to one of the first and second ends 10 and 12 of thecontinuous helical winding 18. The annular ring 64 is believed to reducedistortions to the markers 60 proximate the end or ends of the helicalwinding 18.

Fifth, in the preferred embodiment, where the stent 100 includes acontinuous helical winding 18 and a plurality of circumferentialsections 20 defining a tube having an axial length of about 60millimeters and an outer diameter of about 6 millimeters, at least onebridge 26 is configured to connect two circumferential sections 20together so that the force required to displace a portion of the stent100 between two fixed points located about 30 millimeters apart is lessthan 3.2 Newton for a displacement of about 3 millimeters along an axisorthogonal to the axis 16 of the stent 100. In particular, asillustrated in FIG. 9, the stent 100 is loaded in carrier sheaths 80made of PEBAX, where the stent 100 is supported by an inner catheter 82and outer catheter 84. The outer catheter 84 has an inner diameter ofabout 1.6 millimeters. Both the inner and outer catheters 82 and 84 arecommercially available 6 French catheters under the trade name Luminexx®III manufactured by Angiomed GmbH & Co., Medizintechnik KG of Germany,and available from C.R. Bard, Inc. of Murray Hill, N.J. The twocatheters 82 and 84 with the stent 100 in between are placed on a3-point bending jig where the outer catheter 84 is supported at twolocations spaced apart at distance L of about 30 millimeters. A load F1is placed on the stent 100 proximate the center of the distance L andthe force required to bend the catheters 82 and 84 and the stent 100over a displacement D1 of about 3 millimeters is measured. For the stoat100 of the preferred embodiment illustrated in FIG. 1, the forcerequired to achieve a displacement D1 of 3 millimeters is less than 3.2Newtons. As compared with a known helical stent (sold under the tradename Lifestent® and having an outer diameter of approximately 6millimeters and a length of about 40 millimeters), using the sametesting configuration, the force required to displace the known stent ina Luminexx® III catheter sheath over a distance D1 of approximately 3millimeters is approximately 3.2 Newtons or greater. It is believed thatthe lower the force required to displace the stent (when contained incatheters 82 and 84) a distance D1 (of about 3 millimeters), the betterthe ability of the stent and the catheters to navigate tortuous anatomy.By requiring less than 3.2 Newtons force in this test, the preferredembodiment stent 100 is believed to be highly flexible during deliveryand implantation, as compared to known stents and delivery systems, andthis high flexibility facilitates the ability of the clinician tonavigate a duct or vessel necessary to deliver and implant the stent. Inthe particular embodiment tested, the force F1 for stent 100 wasapproximately 1.7 Newtons for a 6 French Luminexx® III catheter.

Sixth, by virtue of the structures described herein, an advantageoustechnique to load a helical stent 100 is provided that does not havephysical interference between arcuate undulation sections 32 and bridges26 in the compressed configuration of the stent 100 in a generallytubular sheath from an inside diameter of approximately 6 millimeters tothe compressed stent 100 configuration of approximately 2 millimeters (6French). Specifically, where a stent is utilized with approximately 48arcuate undulation sections 32 (which include the struts 28) in eachcircumferential section 20, and 9 bridges 26 for connection to adjacentcircumferential sections 20, it has been advantageously determined thatthe stent 100 does not require a transition portion and a tubular endzone, as is known in the art. In particular, the method can be achievedby utilization of a physical embodiment of the stent 100 (e.g., FIGS.1-5) and compressing the stent 100. The stent 100 has an outsidediameter of approximately 6 millimeters that must be compressed to fitwithin the generally tubular sheath 80 that has an outside diameter ofapproximately 2 millimeters (6 French) and an inside diameter ofapproximately 1.6 millimeters, without any of the struts 28 of the stent100 crossing each other when compressed and inserted into the sheath 80.In other words, in the expanded unimplanted configuration of the stent100, none of the struts 28 and bridges 26 physically interfere with,i.e., overlap or cross, other struts 28 or bridges 26 of the stent 100.The stent 100 can be compressed, without the use of transition strutsegments (or the use of the annular rings 64) at the axial ends of thehelical winding 18, to a smaller outer diameter of about 3 millimetersor less (and preferably less than 2 millimeters) where the innersurfaces of the struts 28 and bridges 26 remain substantially contiguouswithout physical interference of one strut 28 with another strut 28 orwith a bridge 26.

Bio-active agents can be added to the stent (e.g., either by a coatingor via a carrier medium such as resorbable polymers) for delivery to thehost vessel or duct. The bio-active agents can also be used to coat theentire stent. A coating can include one or more non-genetic therapeuticagents, genetic materials and cells and combinations thereof as well asother polymeric coatings.

Non-genetic therapeutic agents include anti-thrombogenic agents such asheparin, heparin derivatives, urokinase, and PPack (dextrophenylalanineproline arginine chloromethylketone); anti-proliferative agents such asenoxaprin, angiopeptin, or monoclonal antibodies capable of blockingsmooth muscle cell proliferation, hirudin, and acetylsalicylic acid;anti-inflammatory agents such as dexamethasone, prednisolone,corticosterone, budesonide, estrogen, sulfasalazine, and mesalamine;antineoplastic/antiproliferative/anti-miotic agents such as paclitaxel,5-fluorouracil, cisplatin, vinblastine, vincristine, epothilones,endostatin, angiostatin and thymidine kinase inhibitors; anestheticagents such as lidocaine, bupivacaine, and ropivacaine; anti-coagulants,an ROD peptide-containing compound, heparin, antithrombin compounds,platelet receptor antagonists, anti-thrombin anticodies, anti-plateletreceptor antibodies, aspirin, prostaglandin inhibitors, plateletinhibitors and tick antiplatelet peptides; vascular cell growthpromotors such as growth factor inhibitors, growth factor receptorantagonists, transcriptional activators, and translational promotors;vascular cell growth inhibitors such as growth factor inhibitors, growthfactor receptor antagonists, transcriptional repressors, translationalrepressors, replication inhibitors, inhibitory antibodies, antibodiesdirected against growth factors, bifunctional molecules consisting of agrowth factor and a cytotoxin, bifunctional molecules consisting of anantibody and a cytotoxin; cholesterol-lowering agents; vasodilatingagents; and agents which interfere with endogenous vascoactivemechanisms.

Genetic materials include anti-sense DNA and RNA, DNA coding for,anti-sense RNA, tRNA or rRNA to replace defective or deficientendogenous molecules, angiogenic factors including growth factors suchas acidic and basic fibroblast growth factors, vascular endothelialgrowth factor, epidermal growth factor, transforming growth factor alphaand beta, platelet-derived endothelial growth factor, platelet-derivedgrowth factor, tumor necrosis factor alpha, hepatocyte growth factor andinsulin like growth factor, cell cycle inhibitors including CDinhibitors, thymidine kinase (“TK”) and other agents useful forinterfering with cell proliferation the family of bone morphogenicproteins (“BMPs”), BMP-2, BMP-3, BMP-4, BMP-5, BMP-6 (Vgr-1), BMP-7(OP-1), BMP-8, BMP-9, BMP-10, BMP-1, BMP-12, BMP-13, BMP-14, BMP-15, andBMP-16. Desirable BMP's are any of BMP-2, BMP-3, BMP-4, BMP-5, BMP-6 andBMP-7. These dimeric proteins can be provided as homodimers,heterodimers, or combinations thereof, alone or together with othermolecules. Alternatively or, in addition, molecules capable of inducingan upstream or downstream effect of a BMP can be provided. Suchmolecules include any of the “hedgehog” proteins, or the DNAs encodingthem.

Cells can be of human origin (autologous or allogeneic) or from ananimal source (xenogeneic), genetically engineered if desired to deliverproteins of interest at the deployment site. The cells can be providedin a delivery media. The delivery media can be formulated as needed tomaintain cell function and viability.

Suitable polymer coating materials include polycarboxylic acids,cellulosic polymers, including cellulose acetate and cellulose nitrate,gelatin, polyvinylpyrrolidone, cross-linked polyvinylpyrrolidone,polyanhydrides including maleic anhydride polymers, polyamides,polyvinyl alcohols, copolymers of vinyl monomers such as EVA, polyvinylethers, polyvinyl aromatics, polyethylene oxides, glycosaminoglycans,polysaccharides, polyesters including polyethylene terephthalate,polyacrylamides, polyethers, polyether sulfone, polycarbonate,polyalkylenes including polypropylene, polyethylene and high molecularweight polyethylene, halogenated polyalkylenes includingpolytetrafluoroethylene, polyurethanes, polyorthoesters, proteins,polypeptides, silicones, siloxane polymers, polylactic acid,polyglycolic acid, polycaprolactone, polyhydroxybutyrate valerate andblends and copolymers thereof coatings from polymer dispersions such aspolyurethane dispersions (for example, BAYHDROL® fibrin, collagen andderivatives thereof, polysaccharides such as celluloses, starches,dextrans, alginates and derivatives, hyaluronic acid, squaleneemulsions. Polyacrylic acid, available as HYDROPLUS® (from BostonScientific Corporation of Natick, Mass.), and described in U.S. Pat. No.5,091,205, the disclosure of which is hereby incorporated herein byreference, is particularly desirable. Even more desirable is a copolymerof polylactic acid and polycaprolactone.

The preferred stents can also be used as the framework for a vasculargraft. Suitable coverings include nylon, collagen, PTFE and expandedPTFE, polyethylene terephthalate, KEVLAR® polyaramid, and ultra-highmolecular weight polyethylene. More generally, any known graft materialcan be used including synthetic polymers such as polyethylene,polypropylene, polyurethane, polyglycolic acid, polyesters, polyamides,their mixtures, blends and copolymers.

In the preferred embodiments, some or all of the bridges 26 can bebio-resorbed while leaving the undulating strut 28 configurationessentially unchanged. In other embodiments, however, the entire stent100 can be resorbed in stages by a suitable coating over the resorbablematerial. For example, the bridges 26 can resorb within a short timeperiod after implantation, such as, for example, 30 days. The remaininghelical stent framework (made of a resorbable material such as metal orpolymers) can thereafter resorb in a subsequent time period, such as,for example, 90 days to 2 years from implantation.

Markers 60 can be provided for all of the embodiments described herein.The marker 60 can be formed from the same material as the stent 100 aslong as the material is radiographic or radiopaque. The marker materialcan also be formed from gold, tantalum, platinum for example. The marker60 can be formed from a marker material different from the material usedto form another marker 60.

The stents described herein can be, with appropriate modifications,delivered to an implantation site in a host with the delivery devicesdescribed and shown in U.S. Patent Application Nos. 2005/0090890 or2002/0183826, U.S. Pat. Nos. 6,939,352 or 6,866,669.

Although the preferred embodiments have been described in relation to aframe work that define a tube using wire like members, other variationsare within the scope of the invention. For example, the frame work candefine different tubular sections with different outer diameters, theframe work can define a tubular section coupled to a conic section, theframe work can define a single cone, and the wire-like members can be incross-sections other than circular such as, for example, rectangular,square, or polygonal.

Even though various aspects of the preferred embodiments have beendescribed as self-expanding Nitinol stents suitable for use in thecommon bile duct or superficial femoral artery, it should be apparent toa person skilled in the art that these improvements can be applied toself-expanding stents of all sizes and made from any suitable material.Further, such stents can be applied to any body lumen where it isdesired to place a structure to maintain patency, prevent occlusivedisease, or for other medical purposes, such as to hold embolizationdevices in place. Further, the features described in the embodiments canbe applied to balloon-expanded stents made from malleable or formablematerials and intended to be expanded inside a suitable body lumen. Thefeatures described in the embodiments can also be applied to bare metalstents, stents made from other than metallic materials, stents with orwithout coatings intended for such purposes as dispensing a medicamentor preventing disease processes, and stents where some or all of thecomponents (e.g., struts, bridges, paddles) of the stents arebio-degradable or bio-resorbable.

The embodiments use the example of a 6 mm self-expanding stent, but canbe applied with equal merit to other kinds of stents and stents of othersizes. Specifically, stents for use in peripheral arteries arecustomarily made in outer diameters ranging from 3 mm to 12 mm, and inlengths from 10 mm to 200 mm. Stents of larger and smaller diameters andlengths can also be made accordingly. Also, stents embodying thefeatures of the embodiments can be used in other arteries, veins, thebiliary system, esophagus, trachea, and other body lumens.

While the present invention has been disclosed with reference to certainembodiments, numerous modifications, alterations, and changes to thedescribed embodiments are possible without departing from the sphere andscope of the present invention, as defined in the appended claims.Accordingly, it is intended that the present invention not be limited tothe described embodiments, but that it has the full scope defined by thelanguage of the following claims, and equivalents thereof.

What is claimed is:
 1. An implantable prosthesis comprising: acontinuous helical winding having a plurality of circumferentialsections circumscribing a helical axis, which is cut by an orthogonalplane, from a first end to a second end to define a tube, the pluralityof circumferential sections being spaced apart along the helical axis,each of the plurality of circumferential sections having anon-orthogonal helical angle relative to the helical axis; at least onebridge configured to connect one circumferential section to anaxially-spaced adjacent circumferential section, the at least one bridgeextending along its entire length on a plane orthogonal to the helicalaxis; at least one annular ring connected to one of the first and secondends of the continuous helical winding, the at least one annular ringorthogonal to the helical axis; and at least one marker having a firstend connected to the at least one annular ring, and a second endconnected to the continuous helical winding, wherein the implantableprosthesis is operable from a contracted state to an expanded state andin the contracted state the at least one bridge creates acircumferential offset between adjacent circumferential sections thatwhen measured in the plane orthogonal to the helical axis is equal tothe length of the at least one bridge and in the expanded state the atleast one bridge maintains the circumferential off-set.
 2. Theimplantable prosthesis of claim 1, wherein the continuous helicalwinding and the at least one bridge are in the expanded state.
 3. Theimplantable prosthesis of claim 1, wherein each of the plurality ofcircumferential sections has a plurality of undulations disposed aboutthe tube.
 4. The implantable prosthesis of claim 3, wherein the at leastone bridge comprises a minimum width greater than a width of anysegments that define the plurality of undulations.
 5. The implantableprosthesis of claim 4, wherein the plurality of undulations comprisezig-zag struts.
 6. The implantable prosthesis of claim 4, wherein theplurality of undulations exhibits a wave pattern.
 7. The implantableprosthesis of claim 6, wherein the implantable prosthesis is composed ofat least one self-expanding material.
 8. The implantable prosthesis ofclaim 7, wherein the at least one self-expanding material is Nitinol. 9.The implantable prosthesis of claim 8, wherein the implantableprosthesis is composed of at least one weak shape memory metal.
 10. Theimplantable prosthesis of claim 9, further comprising a bridge vertexconnecting at least one stent strut to the at least one bridge such thatthe bridge vertex is rigid to isolate the at least one stent strut fromdeformation forces during stent expansion.
 11. The implantableprosthesis of claim 3, wherein the plurality of undulations comprisezig-zag struts.
 12. The implantable prosthesis of claim 3, wherein theplurality of undulations exhibits a wave pattern.
 13. The implantableprosthesis of claim 1, wherein the implantable prosthesis is composed ofat least one self-expanding material.
 14. The implantable prosthesis ofclaim 13, wherein the at least one self-expanding material is Nitinol.15. The implantable prosthesis of claim 1, wherein the implantableprosthesis is composed of at least one weak shape memory metal.
 16. Theimplantable prosthesis of claim 1, further comprising a bridge vertexconnecting at least one stent strut to the at least one bridge such thatthe bridge vertex is rigid to isolate the at least stent strut fromdeformation forces during stent expansion.
 17. The implantableprosthesis of claim 1, wherein the first end of the at least one markerhas a first width, and wherein the second end of the at least one markerhas a second width less than the first width.
 18. The implantableprosthesis of claim 17, wherein the first width extends along a firstsection of the at least one marker, the first section having a generallyrectangular configuration.
 19. The implantable prosthesis of claim 1,wherein the at least one annular ring includes sacrificial locations atconnection points to the at least one marker to facilitate removal ofthe at least one annular ring from the implantable prosthesis.
 20. Animplantable prosthesis having a contracted state and an expanded state,the implantable prosthesis comprising: a continuous helical windingincluding a plurality of circumferential sections having anon-orthogonal helical angle relative to a helical axis; a plurality ofbridges connecting the plurality of circumferential sections, each ofthe plurality of bridges lying in a plane orthogonal to the helical axisalong a length thereof, the plurality of bridges creating acircumferential offset between adjacent circumferential sections in thecontracted state that is maintained in the expanded state; an annularring connected to a first end of the continuous helical winding, theannular ring orthogonal to the helical axis; and a plurality of markershaving a first end connected to the annular ring, the annular ringincluding sacrificial locations at connection points to each of theplurality of markers to facilitate removal of the at least one annularring from the implantable prosthesis.